A study published yesterday in the Proceedings of the National Academy of Sciences indicates that outbreaks of mad cow disease in Europe have triggered a chain of events in the past 40 years that ultimately benefitted grassland birds here in North America.

Here’s how it happened. After European outbreaks of mad cow disease, Europe imported cattle from North America. That meant North America had fewer cattle. Ranchers needed less cattle feed, so farmers harvested less hay. As cities and farms have displaced huge swaths of native prairie, hayfields have become critical habitat for grassland birds -- especially unmowed hayfields.

The Ontario scientists who conducted the study looked at data from 1966 to 2007, and they say the benefits to birds from living in unmowed hayfields didn’t show up right away. But three years after the increase in standing hayfields, 85 percent of grassland bird species had higher populations.

The scientists say their study demonstrates that socioeconomic issues in one region of the world may have profound effects on biodiversity in another. Here in the U-S, as agricultural conservation easements face the budget chopping block, this Mad Cow study may prove to be a cautionary tale for our grassland birds, for many of those easements that might not get funded involve land full of unmowed hay.